It's the time most anticipated by Americans - rich and poor, black and white, kids and adults, from corn country to concrete sidewalks.

It's the night of the week that accounts for more money spent, fewer phone calls, more dates, fewer TV shows watched, more murders, fewer suicides, more diets broken, more dancing in church, and more cats falling from Manhattan windows than any other night.

In ``Saturday Night,'' Orlean takes readers on a whiz-bang tour of several dozen spots where locals whoop it up, workers rake it in, women hunt husbands, dieters binge, prisoners go on dates, and religious people convert. The author turns up tidbits from beneath steeples in the deep South to behind steering wheels on a Midwestern Main Street.

Her report: Whether at work, play, or in prison, Americans ``act differently on Saturday night for no reason other than it's Saturday night.''

Orlean's research is original and ambitious, and her findings wonderfully entertaining. Choosing her two subjects - leisure and average citizens - Orlean bucks America's obsessions with work and celebrity. Yet her characters become stars.

Orlean is a keen observer, a first-rate fly-on-the-wall with a sense of humor and a compassion for humanity. Her study goes beyond activities and gives us the characters who do them. A nation unfolds through the lives and loves of dozens of Americans.

Through conversation, description of dress and local geography, and bits of family history, the writer allows the characters to reveal themselves - sometimes to their own surprise. Orlean is a good reporter; her prose is clean and informative.

But don't expect any tidy conclusion to this study. Instead, Orlean steps back to observe the whole, making that special night a metaphor for life in general: ``Saturday night is mostly mythic: larger than life, more meaningful the less closely it is examined, romantic in the purest way, more an idea than an event.''

Orlean includes historical morsels in each chapter - such as how Saturday Night Specials got their name. (In Detroit, people in need of a gun on Saturday night had to drive across the state line at Toledo, Ohio, where they could pick up the handguns for $3.)

Music is the lifeblood of Saturday night, and many a song revolves around the theme - from the likes of Noel Coward, Sam Cooke, Elton John, the Bay City Rollers. In fact, says Orlean, lyrics themselves changed America's image of Saturday night. ``Saturday night may be sweet and romantic, but in modern terms it is more importantly a time to ditch parents, ... be free of your boss, escape your teachers, ignore social convention, wear weird clothes, ... - in other words, the temporal equivalent of rock and roll.''

Orlean's ambitious study of Americans at leisure in the 1980s deserves a place next to other important sociological works, such as Studs Terkel's ``Working'' and Helen and Robert Lynd's ``Middletown'' (a survey of Indiana in the 1920s and '30s.) But the book suggests more. Would it be too much to ask Ms. Orlean to forfeit another year of Saturday nights and report on, say, Budapest, Bogot'a, and Beijing?